I liked your solution to the nodus problem as applied to the Swenson dial.
In reading about the dial on its web-site, I saw that great care was taken in
accurate placement of the dial's lines.
Could you please tell me how the declination of the wall was determined? I
think that if this value was off by even a tenth of a degree, the errors
introduced would be greater than the 1/16th inch accuracy of the anchor point
placements.
I used two methods:
1) the timing of the sun when it cast a shadows of the end pillars
parallel to wall. This was done several times.
2) One of the engineers at our Facilities Engineering Department surveyed it.
We found the wall was East-West to better than 0.1 degree. Although I
could have easily corrected for it, it wasn't necessary. We suspect
the surveyor who originally laid out the building must have had a
thing about accuracy.
In fact the limiting thing on the wall is not the East-West
alignment, but the vertical flatness. he wall is a brick curtain
attached at each floor. If you get close to the wall and look up you
can see it bows in and out. I decided that to try and correct for
this might be a waste of time as the temperature here varies from -40
to 110 degrees F and so the wall bow will vary.
Could you also elaborate on why a noncartesian system was used to mark the
placement of the anchor points?
-Bill Gottesman
That was an idea of the fabricator/sculptor Gene Olson. I supplied
x-y coordinates with the origin at the base of the Gnomon. Gene who
had a lot of experience with large wall sculptures and signs decided
that it would be best to mount a large boss/stud at the gnomon base
position and use a combination of radial and Cartesian coordinate
system. He generated a table of numbers in Excel which had the radial
distance from the gnomon and the distance from specific points the
horizontal scale at the top of the wall. This simplified the drilling
process. They could drill a series of holes without moving the
rulers, just rotating them. It worked perfectly.
--
Cheers,
John
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